A typical safety ski binding of the above-mentioned type is illustrated in FIGS. 1 to 3 of Austrian Pat. No. 327 759. In this conventional design, the control surface is constructed on the sole holder, the locking member is a rounded portion of the slide member, and the slide member is constructed approximately wedge-shaped as viewed in a side view. The sole holder is supported swingably at the front end region of the bearing block, and the swivel axis of the spring housing is offset rearwardly with respect to the swivel axis of the sole holder. The control surface of the sole holder is designed as a flat surface, and in the downhill skiing position of the heel holder the slide member is supported on the upper end region of the control surface. Through the flat design of the control surface on the sole holder, there results during a release of the heel holder by swinging of the sole holder a dead-center position of the slide member on the control surface, which dead-center position limits the elasticity range. Through this, the tension of the spring in the downhill skiing position and in the open position of the sole holder is approximately the same. By providing the swivel axis of the sole holder at the front end of the bearing block, it is not possible to open the sole holder sufficiently wide for a reasonable height of the binding, so that stepping into the sole holder is difficult. Furthermore, this binding has, due to its construction, only a small elasticity, and there exists due to the whiplike support of the spring housing which receives the slide member a certain danger with respect to injuries during the voluntary opening of the binding, since the spring housing which simultaneously serves as the operating member, after exceeding its dead-center position, tilts under the action of the release spring.
German Offenlegungsschrift No. 31 22 653 illustrates a safety ski binding in which a holding part which carries the sole holder is supported for pivotal movement about an axis which extends transversely to the longitudinal axis of the ski and is arranged on the bearing block. The region of the holding part which lies opposite the sole holder with respect to the swivel axis is designed as a spring housing which receives the release spring which biases a slide member, the slide member being guided movably in the spring housing and cooperating with a camlike elevation which is arranged on the bearing block by means of a control surface which is arranged on its front side. The region of the holding part which receives the release spring serves simultaneously as an operating member for the voluntary opening of the binding. It is disadvantageous in this design that, due to the one-piece design of sole holder and operating member, during a pressing down of the operating plate the sole holder must automatically swing upwardly. Thus, stepping out of the binding, for example by pressing down the holding part with a ski or the ski shoe, is difficult, particularly for a less experienced skier, since there is the danger of losing his or her balance.
In the safety ski binding which is illustrated in FIGS. 1 to 4 of German Offenlegungsschrift No. 27 00 834, a piston which is biased by a release spring is guided movably inside of a bearing block which is arranged on the ski and the piston cooperates by means of a nose with a control surface which is provided on the sole holder. The sole holder is supported pivotally on an axle which is provided on the bearing block, and extends through a free positioning recess in the piston so that movement of the piston is not influenced by the axle. Parallel to the swivel axle of the sole holder there is provided a further axle which is connected fixedly to the piston, on which further axle is supported pivotally a release lever. The swivel axle of the sole holder engages furthermore control recesses which are provided on the sidewalls of the release lever. During an automatic release, for example due to a fall of the skier, the control surface which is on the sole holder moves the piston against the force of the release spring until finally the open position of the sole holder is reached, in which position the release spring can slightly relax. For a voluntary opening of the sole holder, the release lever is pressed down, whereby edges of the control recesses slide on the swivel axle of the sole holder, which causes the piston to be moved back against the force of the release spring. This permits the sole holder, assisted by a spring which urges it in the opening direction, to swing into its open position. Disadvantageous in this design is that, by arranging the release spring and the slide member in the bearing block, which is arranged on the ski, for a voluntary opening of the binding a separate structural part such as the release lever, is needed.
Therefore, a purpose of the invention is to provide a safety ski binding of the above-mentioned type which does not have the disadvantages of conventional designs, which has few structural parts and thus is built compactly and simply, which can be manufactured easily, and which is comfortable for inexperienced skiers to operate.